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In the 15 I would do male endlers live bearers or guppies. In the 29 I would have a pair of sparkling gouramis, a school of glowlight tetras, and some shrimp or pygmy corydoras on the bottom.
Well if he has higher ph like 7.9 to the 8.0s and above, he could get some shelldweller cichlids, or just plain Tanganzanika cichlids, some grow to only 5"